In recent years, new consumer electronics devices have been introduced that can connect to networks such as Local Area Networks (“LANs”) and the like. Examples of such devices include printers, Digital Video Disk (“DVD”) players, personal video recorders, etc. For it to be useful to connect a device, such as a printer, to a network, the device must be able to communicate with other devices on the network. There should be a common “language” or protocol that the devices can use to talk to each other, and a simple way for devices to find each other with as little human intervention as possible. Conventional Universal Plug and Play (“UPnP”) provides for most of these needs.
UPnP defines a category of devices called Media Servers, and another category called Media Renderers, and a concept called a Control Point. A Control Point is an entity which can find UPnP devices and control them. UPnP Media Server devices typically transfer multimedia content (e.g., a digital representation of a movie) to a Media Renderer device. For example, a networked DVD player may be a Media Renderer and a PC-based server maybe a Media Server. The networked DVD player may have a built-in Control Point, which allows it to discover the Media Server and allows it to download a catalog of movies from the Media Server. The Control Point may initiate a streaming transfer of one the movies from the Media Server to the Media Renderer so that it can be shown on a screen (e.g., a TV set) that the Media Renderer is attached to.
UPnP does not specify the format of the multimedia content (the movie in the previous example). However, UPnP does specify how a Media Server device can offer multiple representations of the same content, allowing the Control Point to choose a representation which is suitable for the Media Renderer. For example, the networked DVD player might only be able to play movies which are encoded using Moving Picture Experts Group (“MPEG”)-2 compression. If a movie file which is stored on the server is encoded using Windows Media Video (“WMV”) compression, then the DVD player will only be able to play the movie if the server can offer the movie in MPEG-2 format. Converting the movie from one format to another is called “transcoding”. The quality of the images (or sound) that has been transcoded can be inferior to that of the original non-transcoded content.
In the general case, a Media Renderer might support multiple formats, and a Media Server may offer a movie in several different formats. There may be only partial overlap between the set of formats offered and the set of formats supported by the Media Renderer. It is possible for a Media Server to offer multiple representations of the same content, and each representation might be encoded using the same compression format and only differ by the width and height, or only differ by the encoding bit rate, etc.
Although it would be possible for a Media Renderer to initiate the transfer of multiple media representations until it find one that works, such an approach can be time consuming and may not result in the best user experience. For example, the first representation that “works” might be encoded using a very low bit rate, resulting in a lower than necessary image quality.